JP7230975B1 - Welding joint for electromagnetic steel strip, friction stir welding method, and method for manufacturing electromagnetic steel strip - Google Patents

Abstract

An object of the present invention is to provide a joint for electromagnetic steel strips capable of suppressing breakage of a coil joint in a production line due to deterioration of the mechanical properties and shape of the coil joint.
Kind Code: A1 A ferrite phase-based steel structure is used for each of a joint portion and a heat-work-affected portion, and the relationships of the following formulas (1) to (4) are satisfied.
Dsz≦200 μm (1)
Dhaz1≦Dbm1 (2)
Dhaz2≦Dbm2 (3)
0.9×(Hbm1+Hbm2)/2≦Hsz≦1.2×(Hbm1+Hbm2)/2 (4)
[Selection drawing] Fig. 1

Description

TECHNICAL FIELD The present invention relates to a welded joint for an electromagnetic steel strip, a friction stir welding method, and a method for manufacturing an electromagnetic steel strip.

In steel sheet production lines, for example, pickling, cold rolling, annealing, and plating production lines, in order to improve productivity and yield, so-called coil joining is performed before the steel strip is threaded. is common. Here, the coil joining refers to the end (rear end) of the preceding steel strip (hereinafter also referred to as the preceding steel strip) and the steel strip following the preceding steel strip (hereinafter also referred to as the following steel strip) in the production line. ) (hereinbelow, a joint formed by coil joining is also referred to as a coil joint). Note that the tip is the end of the steel strip on the traveling direction side in the production line. Also, the rear end is the end opposite to the direction of travel of the steel strip in the production line. By performing this coil joining, it becomes possible to roll the steel strip while applying tension over the entire length of the steel strip. In addition, it is possible to control the thickness and shape of the steel strip at the front end and rear end with high accuracy.

Conventionally, flash butt welding or the like has generally been applied to coil joining. However, with advances in laser welding machines, the application of laser welding to coil joining is becoming mainstream, for example, even in production lines for electromagnetic steel sheets, stainless steel sheets, and high-tensile steel sheets.

As such a technique, for example, in Patent Document 1,
When welding high-Si steel, a filler wire whose main component is Ni or a filler powder whose main component is Ni is supplied so that the chemical composition of the weld metal satisfies the following formula (1). A laser welding method for high Si steel characterized by performing
X = [% Ni] - [% Si] x 2.5 - ([% Cr] + [% Mo]) x 0.4 ≥ 0 (1)
However, [%Ni], [%Si], [%Cr] and [%Mo] represent the contents (% by weight) of Ni, Si, Cr and Mo in the weld metal, respectively. ”
is disclosed.

In Patent Document 2,
"In a method of laser welding a leading plate and a trailing plate against each other using a filler wire, the ratio of the butt gap (Gap) between the leading plate and the trailing plate at the initial stage of welding to the average width of the weld metal (DEPO) A laser welding method characterized in that (Gap/DEPO) is 0.3 to 0.8."
is disclosed.

In Patent Document 3,
"In the weld formed by laser-welding the leading thin plate and the trailing thin plate made of special steel that are conveyed on a continuous cold rolling line,
Let L1 be the minimum thickness of the base material existing below the upper extension part made of the weld metal that extends to the upper surface side of the base material by cold rolling, and extends to the lower surface side of the base material by cold rolling. Welding of thin plates characterized in that at least one of L1 and L2 is greater than zero, where L2 is the minimum thickness of the base material sandwiched between the lower extension and the upper extension made of weld metal. Department. ”
is disclosed.

JP-A-5-305466 JP 2004-25284 A JP 2011-140026 A Japanese Patent Publication No. 07-505090 Patent No. 3261433 Patent No. 4838385 Patent No. 4838388

Cui, L.; Fujii, H.; Tsuji, N.; Nogi, K. Scripta Mater. 2007, 56, p.637-640.

However, since laser welding is fusion welding, embrittlement occurs due to segregation of impurities during melting and solidification, and embrittlement due to hydrogen penetration, leading to deterioration of the mechanical properties of the joint (weld part). Sometimes. In particular, since the composition of the electrical steel sheet contains a large amount of Si, the mechanical properties of the coil joint tend to deteriorate significantly. Therefore, as in Patent Documents 1 to 3, when laser welding is applied for coil joining of electromagnetic steel strips, breakage occurs at the coil joint in a production line, for example, a continuous cold rolling line, and productivity is reduced due to line stoppage. There was a problem of causing a decrease in

DISCLOSURE OF THE INVENTION The present invention has been developed to solve the above-mentioned problems, and can suppress the occurrence of breakage of coil joints in a production line due to deterioration of the mechanical properties and shape of the coil joints. , to provide a joint for electromagnetic steel strips.
Another object of the present invention is to provide a friction stir welding method for the electromagnetic steel strips for obtaining the welded joint of the electromagnetic steel strips. A further object of the present invention is to provide a method for producing an electromagnetic steel strip using the friction stir welding method for an electromagnetic steel strip.

The inventors have made extensive studies in order to achieve the above object. First, the inventors investigated and examined the reasons why the mechanical properties and shape of the coil joint deteriorate when laser welding is applied to the coil joint of the electromagnetic steel strip, and obtained the following findings. rice field.

(a) As described above, the chemical composition of the electrical steel sheet contains a large amount of Si, specifically about 2.0 to 5.0% by mass. Si is a ferrite stabilizing element. Therefore, when general laser welding is applied to coil joining of electromagnetic steel strips, the ferrite crystal grains of the coil joint portion, which is the fusion zone, and further the ferrite crystal grains of the heat affected zone are coarsened. As a result, the mechanical properties of the coil joints, particularly the toughness and bending strength, are significantly degraded, leading to breakage of the coil joints in the production line.

(b) In addition, in the techniques of Patent Documents 1 to 3 described above, a filler material containing Ni, which is an austenite stabilizing element, as a main component is used. Therefore, the austenite phase is mainly obtained at the coil joint. However, in the techniques of Patent Documents 1 to 3 described above, the variation in the butt gap between the leading steel strip and the trailing steel strip is eliminated, and the amount of fusion of the filler material and the amount of fusion of the steel plate in the fusion zone (weld metal) must be strictly controlled, and the balance between the Ni equivalent and the Cr equivalent in the fusion zone (weld metal) must be properly controlled at all times. That is, unless the balance between the Ni equivalent and the Cr equivalent in the fusion zone (weld metal) is properly controlled, the martensite phase, which is a hard and brittle structure, is formed at the coil joint. This significantly degrades the mechanical properties of the coil joint, especially the toughness. Further, in the heat affected zone, the coarsening of the ferrite crystal grains significantly deteriorates the mechanical properties of the coil joint. For these reasons, breakage of coil joints occurs in the production line.
Here, the Ni equivalent and Cr equivalent are defined by the following equations.
Ni equivalent = [%Ni] + 30 x [%C] + 0.5 x [%Mn]
Cr equivalent = [% Cr] + [% Mo] + 1.5 x [% Si] + 0.5 x [% Nb]
where [%Ni], [%C], [%Mn], [%Cr], [%Mo], [%Si] and [%Nb] are respectively Ni, C, Mn, Cr, Mo, Si and Nb contents (% by mass).

(c) Furthermore, the variation in the butt gap between the preceding steel strip and the following steel strip affects the height of the weld reinforcement. For example, if the welding portion has an excessively convex shape due to the height of the weld reinforcement, stress is concentrated on the weld toe when a load is applied to the welding portion. Therefore, the variation in the abutment gap between the leading steel strip and the trailing steel strip described above also causes breakage of the coil joints in the production line. Although the surplus of the welded portion can be removed by grinding or the like, such an increase in the number of steps causes a significant decrease in productivity.

Based on the above points, the inventors further conducted various studies, and as a result, the inventors came up with the idea of applying friction stir welding for coil welding of electromagnetic steel strips.
Here, the friction stir welding is solid phase welding utilizing frictional heat between a rotary tool and the material to be welded and plastic flow of the material to be welded. That is, the unwelded portion (to-be-welded region) of the material to be welded is friction-stirred by a rotating tool. When the unjoined portion of the material to be joined is heated by frictional heat, plastic flow starts. Then, the interface between the plastic flow region and the base material portion is greatly elongated. As a result, clean interfaces free of oxide come into contact with each other, and a joint is formed without melting the materials to be joined. Here, the welded portion is a region that is subjected to hot working due to frictional heat and plastic flow between the rotary tool and the material to be welded and becomes a recrystallized structure, and is sometimes called an agitated portion. Also, in the region adjacent to the joint, although it is affected by hot working due to frictional heat and plastic flow, there is formed a region where the temperature and working are insufficient and the structure does not lead to recrystallization. This area is called the thermal processing affected zone. Furthermore, the materials to be joined also have areas that are not affected by hot working due to frictional heat and plastic flow. This region is called a base material portion. Techniques related to friction stir welding are disclosed, for example, in Patent Documents 4 to 7 and Non-Patent Document 1, but none of these are applicable to coil welding of electromagnetic steel strips.

Based on the above ideas, the inventors have made various studies and obtained the following findings.
(d) In order to advantageously solve the above problems (a) to (c), friction stir welding is applied as coil welding of electromagnetic steel strips, and the steel structure of the welded part and the heat-affected part is mainly ferrite. and simultaneously achieve refinement of the steel structure of the joint and the thermal processing-affected zone and reduction of the hardness difference between the joint and the base material. Specifically, the following formulas (1) to (4 ) at the same time.
As a result, even when an electromagnetic steel strip is used as the material to be joined, the mechanical properties of the coil joint are improved without causing deterioration in the shape of the coil joint, and breakage of the coil joint in the production line is prevented. effectively suppressed.
Dsz≦200 μm (1)
Dhaz1≦Dbm1 (2)
Dhaz2≦Dbm2 (3)
0.9×(Hbm1+Hbm2)/2≦Hsz≦1.2×(Hbm1+Hbm2)/2 (4)
here,
Dsz is the average value (μm) of the ferrite grain size at the junction;
Dhaz1 is the average value (μm) of the ferrite grain size in the heat-affected zone on the first electromagnetic steel strip side;
Dhaz2 is the average value (μm) of the ferrite grain size in the heat-affected zone on the second electromagnetic steel strip side;
Dbm1 is the average value (μm) of the ferrite grain size in the base metal portion of the first electromagnetic steel strip;
Dbm2 is the average value (μm) of the ferrite grain size in the base metal portion of the second electromagnetic steel strip;
Hsz is the average hardness of the joint,
Hbm1 is the average hardness of the base metal portion of the first magnetic steel strip, and Hbm2 is the average hardness of the base metal portion of the second magnetic steel strip.

(e) Moreover, it is preferable to satisfy the relationships of the following equations (5) and (6) after satisfying the relationships of the above equations (1) to (4) at the same time. As a result, even when an electromagnetic steel strip is used as the material to be joined, the mechanical properties of the coil joint are improved without causing deterioration in the shape of the coil joint, and breakage of the coil joint in the production line is prevented. more effectively deterred.
0.8×TbmL≦TszL (5)
TszH≦1.3×TbmH (6)
here,
TszL is the minimum thickness of the joint (mm);
TszH is the maximum thickness of the joint (mm);
TbmL is the plate thickness (mm) of the thinner one of the first magnetic steel strip and the second magnetic steel strip,
TbmH is the plate thickness (mm) of the thicker magnetic steel strip of the first magnetic steel strip and the second magnetic steel strip;
is. However, when the plate thicknesses of the first magnetic steel strip and the second magnetic steel strip are the same, TbmL=TbmH.

(f) Furthermore, from the viewpoint of increasing the welding speed while suppressing the occurrence of defects, it is preferable to apply so-called double-sided friction stir welding as the friction stir welding.
The present invention has been completed based on the above findings and further studies.

That is, the gist and configuration of the present invention are as follows.
1. An electromagnetic steel strip joining joint for joining a first electromagnetic steel strip and a second electromagnetic steel strip,
The joint of the electromagnetic steel strip has a joint and a thermal processing affected zone adjacent to the joint,
The steel structures of the joint and the thermal processing affected zone are structures mainly composed of ferrite phase,
A joint for electromagnetic steel strips that satisfies the relationships of the following formulas (1) to (4).
Dsz≦200 μm (1)
Dhaz1≦Dbm1 (2)
Dhaz2≦Dbm2 (3)
0.9×(Hbm1+Hbm2)/2≦Hsz≦1.2×(Hbm1+Hbm2)/2 (4)
here,
Dsz is the average value (μm) of the ferrite grain size at the junction;
Dhaz1 is the average value (μm) of the ferrite grain size in the heat-affected zone on the first electromagnetic steel strip side;
Dhaz2 is the average value (μm) of the ferrite grain size in the heat-affected zone on the second electromagnetic steel strip side;
Dbm1 is the average value (μm) of the ferrite grain size in the base metal portion of the first electromagnetic steel strip;
Dbm2 is the average value (μm) of the ferrite grain size in the base metal portion of the second electromagnetic steel strip;
Hsz is the average hardness of the joint,
Hbm1 is the average hardness of the base metal portion of the first magnetic steel strip, and Hbm2 is the average hardness of the base metal portion of the second magnetic steel strip.

2. 2. A welded joint for electromagnetic steel strips according to 1 above, which satisfies the relationships of the following expressions (5) and (6).
0.8×TbmL≦TszL (5)
TszH≦1.3×TbmH (6)
here,
TszL is the minimum thickness of the joint (mm);
TszH is the maximum thickness of the joint (mm);
TbmL is the plate thickness (mm) of the thinner one of the first magnetic steel strip and the second magnetic steel strip,
TbmH is the plate thickness (mm) of the thicker magnetic steel strip of the first magnetic steel strip and the second magnetic steel strip;
is. However, when the plate thicknesses of the first magnetic steel strip and the second magnetic steel strip are the same, TbmL=TbmH.

3. A friction stir welding method for an electromagnetic steel strip, which joins a first electromagnetic steel strip and a second electromagnetic steel strip following the first electromagnetic steel strip in a continuous cold rolling line, comprising:
Pressing a rotating tool against the butted portion or the unjoined portion, which is the overlapping portion, between the end portion of the first electromagnetic steel strip and the end portion of the second electromagnetic steel strip, and
Next, by moving the rotary tool in the joining direction, the first electromagnetic steel strip and the second electromagnetic steel strip are joined,
The steel structures of the joined portion and the heat-affected zone formed by joining the first electromagnetic steel strip and the second electromagnetic steel strip each have a structure mainly composed of ferrite phase, and the following equations (1) to ( 4) A friction stir welding method for electromagnetic steel strips, wherein welding is performed under conditions that satisfy the relationship of 4).
Dsz≦200 μm (1)
Dhaz1≦Dbm1 (2)
Dhaz2≦Dbm2 (3)
0.9×(Hbm1+Hbm2)/2≦Hsz≦1.2×(Hbm1+Hbm2)/2 (4)
here,
Dsz is the average value (μm) of the ferrite grain size at the junction;
Dhaz1 is the average value (μm) of the ferrite grain size in the heat-affected zone on the first electromagnetic steel strip side;
Dhaz2 is the average value (μm) of the ferrite grain size in the heat-affected zone on the second electromagnetic steel strip side;
Dbm1 is the average value (μm) of the ferrite grain size in the base metal portion of the first electromagnetic steel strip;
Dbm2 is the average value (μm) of the ferrite grain size in the base metal portion of the second electromagnetic steel strip;
Hsz is the average hardness of the joint,
Hbm1 is the average hardness of the base metal portion of the first magnetic steel strip, and Hbm2 is the average hardness of the base metal portion of the second magnetic steel strip.

4. 3. The friction stir welding method for electromagnetic steel strips according to 3 above, wherein the welding is performed under conditions satisfying the relationships of the following expressions (5) and (6).
0.8×TbmL≦TszL (5)
TszH≦1.3×TbmH (6)
here,
TszL is the minimum thickness of the joint (mm);
TszH is the maximum thickness of the joint (mm);
TbmL is the plate thickness (mm) of the thinner one of the first magnetic steel strip and the second magnetic steel strip,
TbmH is the plate thickness (mm) of the thicker magnetic steel strip of the first magnetic steel strip and the second magnetic steel strip;
is. However, when the plate thicknesses of the first magnetic steel strip and the second magnetic steel strip are the same, TbmL=TbmH.

5. 5. The friction stir welding method for electromagnetic steel strips according to 3 or 4 above, which is double-sided friction stir welding.

6. a step of joining a first electromagnetic steel strip and a second electromagnetic steel strip by the friction stir welding method for electromagnetic steel strips according to any one of 3 to 5 above to obtain a joined steel strip;
cold-rolling the joined steel strip to obtain a cold-rolled steel strip.

According to the present invention, even when an electromagnetic steel strip is used as the material to be joined, the mechanical properties and shape of the coil joint do not deteriorate, and the coil joint does not break on the production line. effectively suppressed. As a result, the productivity of the electrical steel sheet can be further improved, and the industrial utility value is extremely large. The term "magnetic steel strip" as used herein mainly means an intermediate product.

1 is a schematic diagram of a joint of electromagnetic steel strips according to an embodiment of the present invention; FIG. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram for explaining a friction stir welding method for electromagnetic steel strips according to an embodiment of the present invention, and is a side perspective view showing an example of butt welding by a single-sided friction stir welding method. FIG. 2B is a view taken along line AA of FIG. 2A. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic explaining the friction stir welding method of an electromagnetic steel strip according to one Embodiment of this invention, and is a side perspective view which shows an example of lap joining by a single-sided friction stir welding method. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic explaining the friction stir welding method of the electromagnetic steel strip according to one Embodiment of this invention, and is a side perspective view which shows an example of butt welding by a double-sided friction stir welding method. FIG. 3B is a view taken along line AA of FIG. 3A; It is a schematic diagram which shows an example of the shape of the rotating tool used with a single-sided friction stir welding method. It is a schematic diagram which shows an example of the shape of the rotating tool used with a single-sided friction stir welding method. It is a schematic diagram which shows an example of the shape of the rotating tool used with a single-sided friction stir welding method. It is a schematic diagram which shows an example of the shape of the rotating tool used by a double-sided friction stir welding method. It is a schematic diagram which shows an example of the shape of the rotating tool used by a double-sided friction stir welding method. It is a schematic diagram which shows an example of the shape of the rotating tool used by a double-sided friction stir welding method.

The present invention will be described based on the following embodiments.
[1] Electromagnetic Steel Strip Joining Joint First, an electromagnetic steel strip joining joint according to an embodiment of the present invention will be described with reference to FIG. In the figure, reference numeral 1 is the first electromagnetic steel strip (material to be welded), 2 is the second electromagnetic steel strip (material to be welded), 4 is the joint, and 4-1 is the thermal processing affected zone (first electromagnetic steel strip side), and 4-2 is the thermal processing affected zone (second electromagnetic steel strip side). In addition, FIG. 1 is a cross-sectional view in the plate thickness direction of a joint of electromagnetic steel strips. In the figure, the vertical direction is the plate thickness direction. The horizontal direction is a direction perpendicular to the joining direction and perpendicular to the plate thickness direction (hereinafter also referred to as a joining vertical direction). The direction toward the front side of the paper is the joining direction. That is, the plane shown in FIG. 1 (the cross section in the plate thickness direction here) includes the joining vertical direction and the plate thickness direction.

A joint of electromagnetic steel strips according to one embodiment of the present invention comprises:
An electromagnetic steel strip joining joint for joining a first electromagnetic steel strip and a second electromagnetic steel strip,
The joint of the electromagnetic steel strip has a joint and a thermal processing affected zone adjacent to the joint,
The steel structures of the joint and the thermal processing affected zone are structures mainly composed of ferrite phase,
It satisfies the relationships of the following expressions (1) to (4).
Dsz≦200 μm (1)
Dhaz1≦Dbm1 (2)
Dhaz2≦Dbm2 (3)
0.9×(Hbm1+Hbm2)/2≦Hsz≦1.2×(Hbm1+Hbm2)/2 (4)
here,
Dsz is the average value (μm) of the ferrite grain size at the junction;
Dhaz1 is the average value (μm) of the ferrite grain size in the heat-affected zone on the first electromagnetic steel strip side;
Dhaz2 is the average value (μm) of the ferrite grain size in the heat-affected zone on the second electromagnetic steel strip side;
Dbm1 is the average value (μm) of the ferrite grain size in the base metal portion of the first electromagnetic steel strip;
Dbm2 is the average value (μm) of the ferrite grain size in the base metal portion of the second electromagnetic steel strip;
Hsz is the average hardness of the joint,
Hbm1 is the average hardness of the base metal portion of the first magnetic steel strip, and Hbm2 is the average hardness of the base metal portion of the second magnetic steel strip.

[Materials to be joined (first electromagnetic steel strip and second electromagnetic steel strip)]
The first electromagnetic steel strip and the second electromagnetic steel strip are electromagnetic steel strips to be joined. The chemical compositions of the first magnetic steel strip and the second magnetic steel strip are not particularly limited as long as they are general cold-rolled magnetic steel strips (magnetic steel sheets).

As a chemical composition of such an electrical steel strip, a chemical composition containing Si in the range of 2.0 to 5.0% by mass can be exemplified. In addition, C: 0.005% by mass or less, Si: 2.0 to 5.0% by mass, Al: 3.0% by mass or less, Mn: 2.00% by mass or less, P: 0.2% by mass or less, A component composition of S: 0.01% by mass or less, N: 0.01% by mass or less, and the balance being Fe and unavoidable impurities can be exemplified. In addition, in the above component composition, in mass%, optionally, Sn: 0.2% or less, Sb: 0.2% or less, Ca: 0.01% or less, REM: 0.05% or less, and Mg: At least one selected from the group consisting of 0.01% or less can be contained. Furthermore, the above component composition may optionally contain at least one selected from the group consisting of Cr: 1% or less, Ni: 1% or less, and Cu: 1% or less in mass%. .
Also, the chemical composition of the first magnetic steel strip and the second magnetic steel strip may be the same or different.

The thickness t1 of the first magnetic steel strip and the thickness t2 of the second magnetic steel strip are not particularly limited, but t1 and t2 are preferably 1.2 to 3.2 mm. Note that t1 and t2 may be the same or different.

In addition, in the first and second magnetic steel strips, which are the materials to be welded, regions that are not affected by hot working due to frictional heat and plastic flow are called base material portions.

Also, the base material portion, and the joint portion and the thermal processing affected zone, which will be described later, are defined as follows.
That is, the joint of the electromagnetic steel strip is cut in the plate thickness (vertical) direction so that the plane shown in FIG. Next, the cut surface is polished and etched with a saturated aqueous solution of picric acid, nital (a solution of nitric acid and ethanol) or aqua regia (a mixed solution of concentrated hydrochloric acid and concentrated nitric acid at a volume ratio of 3:1). Then, the cut surface is observed with an optical microscope, and the base material portion, the joint portion, and the thermal processing affected portion are defined based on the degree of etching and the like.

[Joint]
The welded portion is a region that undergoes hot working due to frictional heat and plastic flow between the rotating tool and the material to be welded and becomes a recrystallized structure.

The joint portion is composed of a ferrite phase-based steel structure, specifically, a ferrite phase having an area ratio of 95% or more. The area ratio of the ferrite phase may be 100%. Also, the area ratio of the residual structure other than the ferrite phase is 5% or less. Examples of residual structures other than the ferrite phase include secondary phases such as martensite, sulfides, nitrides, and carbides. The area ratio of the residual tissue may be 0%.

In addition, the area ratio of the ferrite phase is measured as follows.
That is, a test piece is cut out from the joint of the electromagnetic steel strip so that the measurement area of the joint, which will be described later, is included in the observation surface. The observation plane is the plane shown in FIG. 1 (that is, the plane including the joining vertical direction and the plate thickness direction). Then, after polishing the observation surface of the test piece, 3 vol. % nital, a picric acid saturated aqueous solution, or aqua regia to expose the tissue. Then, within the measurement area of the joint portion described later, a total of 10 fields of view are photographed with an optical microscope at a magnification of 500 times. Next, the area of the ferrite phase is calculated for 10 fields of view from the obtained tissue image using Adobe Photoshop of Adobe Systems. Next, the area of the ferrite phase calculated for each field of view is divided by the area of each field of view and multiplied by 100. Then, the arithmetic mean value of those values is taken as the area ratio of the ferrite phase.

In addition, the steel structure of the joint is refined. Satisfying relationships are important. As a result, even when an electromagnetic steel strip is used as the material to be joined, the mechanical properties of the coil joint are improved without causing deterioration in the shape of the coil joint, and breakage of the coil joint in the production line is prevented. effectively suppressed.
Dsz≦200 μm (1)
here,
Dsz is the average value (μm) of the ferrite grain size at the junction;
is.

Here, Dsz is measured according to JIS G 0551. Specifically, it is measured as follows.
That is, the joint of the electromagnetic steel strip is cut in the plate thickness (vertical) direction so that the plane shown in FIG. In the cut plane, the direction perpendicular to the joint is the X-axis, and the plate thickness direction is the Y-axis. Then, at the center position of the joint in the joint vertical direction (for example, in the case of a butt joint, it is the center position of the butt gap, and in the case of a lap joint, it is the center position of the overlapping part), and the plate The plate thickness center position of the material to be joined in the thickness (vertical) direction (for example, in the case of a butt joint, the plate thickness center position of the first electromagnetic steel strip or the second electromagnetic steel strip, whichever has the smaller thickness) and in the case of a lap joint, the center position of the plate thickness of the lapped portion) is set as the origin of the X-axis and the Y-axis. An area of X=-0.2×t to +0.2×t and Y=-0.2×t to +0.2×t is defined as a measurement area. Here, t is the average value (mm) of the plate thickness of the first magnetic steel strip and the plate thickness of the second magnetic steel strip. However, if the above measurement area includes an area that is not a joint, such as a thermal processing affected zone or a base material, the area is excluded from the measurement area. As for the X-axis and the Y-axis, + and - may be arbitrarily set.
Then, at an arbitrary position in the above measurement area, a cutting method (the number of grains captured per 1 mm of the test line or the number of intersections P Evaluation), the ferrite grain size at the junction is measured five times in total, and the average value of these measurements is taken as Dsz. In addition, the measurement area of the ferrite grain size of the joint is hereinafter simply referred to as the measurement area of the joint.

Moreover, it is important to reduce the difference in hardness between the joint and the base material, specifically, to satisfy the relationship of the following formula (4). As a result, even when an electromagnetic steel strip is used as the material to be joined, the mechanical properties of the coil joint are improved without causing deterioration in the shape of the coil joint, and breakage of the coil joint in the production line is prevented. effectively suppressed.
0.9×(Hbm1+Hbm2)/2≦Hsz≦1.2×(Hbm1+Hbm2)/2 (4)
here,
Hsz is the average hardness of the joint,
Hbm1 is the average hardness of the base metal portion of the first magnetic steel strip, and Hbm2 is the average hardness of the base metal portion of the second magnetic steel strip.

Here, Hsz, Hbm1 and Hbm2 are measured according to JIS Z 2244. Specifically, each is measured as follows.
That is, the Vickers hardness (HV) is measured at arbitrary five points within the measurement region of the joint on the cut surface under the condition of a test force of 4.9N. And let these average values be Hsz.
Further, in the above cut surface, within the area of the plate thickness center position ±0.2 × t1 (the level of the plate thickness (vertical) direction) of the base material portion of the first electromagnetic steel strip, and in the second electromagnetic Vickers under the condition of a test force of 4.9 N at any five locations within the thickness center position ± 0.2 × t2 area (thickness (vertical) direction) of the base material of the steel strip. Measure the hardness (HV). Note that the position in the vertical (horizontal) direction of joining may be selected arbitrarily as long as it is the base material portion. Then, the average values of the Vickers hardness (HV) measured in the base metal portion of the first magnetic steel strip and the base metal portion of the second magnetic steel strip are defined as Hbm1 and Hbm2, respectively. Here, t1 and t2 are the plate thicknesses of the first and second magnetic steel strips, respectively.

Although the thickness of the joint is not particularly limited, the relationship between the thicknesses of the first magnetic steel strip and the second magnetic steel strip is appropriately controlled. Specifically, the following formula (5 ) and (6) are preferably satisfied. As a result, even when an electromagnetic steel strip is used as the material to be joined, the mechanical properties of the coil joint are improved without causing deterioration in the shape of the coil joint, and breakage of the coil joint occurs on the production line. can be suppressed more effectively.
0.8×TbmL≦TszL (5)
TszH≦1.3×TbmH (6)
here,
TszL is the minimum thickness of the joint (mm);
TszH is the maximum thickness of the joint (mm);
TbmL is the plate thickness (mm) of the thinner one of the first magnetic steel strip and the second magnetic steel strip,
TbmH is the plate thickness (mm) of the thicker magnetic steel strip of the first magnetic steel strip and the second magnetic steel strip;
is. However, when the plate thicknesses of the first magnetic steel strip and the second magnetic steel strip are the same, TbmL=TbmH.

In addition, TszL and TszH are, for example, the plate thickness (vertical ) direction, and the cut surface is measured using a vernier caliper or the like.

[Thermal processing affected zone]
The heat-work-affected zone is a region adjacent to the joint, which is affected by hot working due to frictional heat and plastic flow but does not reach a recrystallized structure due to insufficient temperature and working. Also, the thermal processing affected zones are formed on both sides of the first magnetic steel strip and the second magnetic steel strip adjacent to the joint.

The thermal processing affected zone is composed of a ferrite phase-based steel structure, specifically, a ferrite phase with an area ratio of 95% or more, as with the joint zone. The area ratio of the ferrite phase may be 100%. Also, the area ratio of the residual structure other than the ferrite phase is 5% or less. Examples of residual structures other than the ferrite phase include secondary phases such as martensite, sulfides, nitrides, and carbides. The area ratio of the residual tissue may be 0%. The area ratio of the ferrite phase may be measured in the same manner as described above.

Also, in the heat-work-affected zone, the steel structure is refined. ) relationship is important.
Dhaz1≦Dbm1 (2)
Dhaz2≦Dbm2 (3)
here,
Dhaz1 is the average value (μm) of the ferrite grain size in the heat-affected zone on the first electromagnetic steel strip side;
Dhaz2 is the average value (μm) of the ferrite grain size in the heat-affected zone on the second electromagnetic steel strip side;
Dbm1 is the average value (μm) of the ferrite grain size in the base metal portion of the first electromagnetic steel strip;
Dbm2 is the average value (μm) of the ferrite grain size in the base metal portion of the second electromagnetic steel strip;
is.

Here, Dhaz1, Dhaz2, Dbm1 and Dbm2 are measured in accordance with JIS G 0551 in the same manner as Dsz, which is the average value of ferrite grain sizes in the joint.
In addition, the measurement area of the ferrite grain size in the heat-affected zone on the first electromagnetic steel strip side (hereinafter also referred to as the measurement area on the heat-affected zone on the first electromagnetic steel strip side) is set as follows. . That is, the joint of the electromagnetic steel strip is cut in the plate thickness (vertical) direction so that the plane shown in FIG. In the above cut plane, the direction perpendicular to the joint is the X-axis, and the plate thickness direction is the Y-axis. The origin of the X-axis and the Y-axis is defined as the boundary position between the joint portion at the plate thickness center position (level) of the first electromagnetic steel strip and the heat-affected zone on the side of the first electromagnetic steel strip. Regarding the X axis, the first electromagnetic steel strip side is + and the joint side is -, and the area of X = 0 to +0.4 × t1 and Y = -0.2 × t1 to +0.2 × t1 is measured. area. Here, t1 is the plate thickness of the first electromagnetic steel strip. As for the Y-axis, + and - may be arbitrarily set. However, if the above measurement region includes a region that is not a heat-work-affected zone on the side of the first electrical steel strip, such as a joint portion or base metal portion, the region is excluded from the measurement region.
As described above, the welded portion refers to a region that undergoes hot working due to frictional heat and plastic flow between the rotating tool and the material to be welded and becomes a recrystallized structure. The heat-work-affected zone is a region adjacent to the joint and is affected by hot working due to frictional heat and plastic flow, but is a region where the temperature and working are insufficient and the structure does not lead to recrystallization. The base material refers to a region that is not affected by hot working due to frictional heat and plastic flow.

Similarly, the measurement area of the ferrite grain size in the heat-affected zone of the second electromagnetic steel strip (hereinafter also referred to as the measurement area of the heat-affected zone of the second electromagnetic steel strip) is set as follows. do. That is, the joint of the electromagnetic steel strip is cut in the plate thickness (vertical) direction so that the plane shown in FIG. In the above cut plane, the direction perpendicular to the joint is the X-axis, and the plate thickness direction is the Y-axis. The origin of the X-axis and the Y-axis is defined as the boundary position between the joint portion at the plate thickness center position (level) of the second electromagnetic steel strip and the heat-affected zone on the side of the second electromagnetic steel strip. Regarding the X axis, the second magnetic steel strip side is + and the joint side is -, and the area of X = 0 to +0.4 x t2 and Y = -0.2 x t2 to +0.2 x t2 is measured. area. Here, t2 is the plate thickness of the second electromagnetic steel strip. As for the Y-axis, + and - may be arbitrarily set. However, if the above measurement region includes a region that is not a heat-work-affected zone on the side of the second electrical steel strip, such as a joint or a base material, the region is excluded from the measurement region.

In addition, the measurement area of the ferrite grain size of the base material portion of the first electromagnetic steel strip and the second electromagnetic steel strip (hereinafter referred to as the measurement area of the base material portion of the first electromagnetic steel strip and the second electromagnetic steel strip) ) are the thickness center position ±0.2 × t1 area (level in the thickness (vertical) direction) of the base material portion of the first electromagnetic steel strip in the above cut surface and the second electromagnetic steel strip of the thickness center position of the base material portion ±0.2×t2 (level in the thickness (vertical) direction). Note that the position in the vertical (horizontal) direction of joining may be selected arbitrarily as long as it is the base material portion. Here, t1 and t2 are the plate thicknesses of the first and second magnetic steel strips, respectively.

Examples of joint types include butt joints and lap joints.

[2] Friction Stir Welding Method for Electrical Steel Strips Next, a friction stir welding method for electrical steel strips according to an embodiment of the present invention will be described.
As described above, the friction stir welding method for electromagnetic steel strips according to one embodiment of the present invention applies friction stir welding as coil welding of electromagnetic steel strips, and then converts the steel structure of the joint and the heat-affected zone to ferrite. It is characterized by making the structure of the main body and refining the steel structure of the joint and the heat-affected zone to reduce the difference in hardness between the joint and the base material.
More specifically, the friction stir welding method for electromagnetic steel strips according to one embodiment of the present invention includes:
A friction stir welding method for an electromagnetic steel strip, which joins a first electromagnetic steel strip and a second electromagnetic steel strip following the first electromagnetic steel strip in a continuous cold rolling line, comprising:
Pressing a rotating tool against the butted portion or the unjoined portion, which is the overlapping portion, between the end portion of the first electromagnetic steel strip and the end portion of the second electromagnetic steel strip, and
Next, by moving the rotary tool in the joining direction, the first electromagnetic steel strip and the second electromagnetic steel strip are joined,
The steel structures of the joined portion and the heat-affected zone formed by joining the first electromagnetic steel strip and the second electromagnetic steel strip are respectively composed mainly of ferrite phase, and the above formulas (1) to The bonding is performed under the condition that the relationship (4) is satisfied.

Suitable examples of joint types include butt joints and lap joints.
In the butt joint, the first electromagnetic steel strip and the second electromagnetic steel strip are joined with the end surfaces of the first electromagnetic steel strip and the second electromagnetic steel strip facing each other as shown in FIGS. 2A and 2B. A rotary tool is rotated and pressed against the abutting portion including the end face (abutting surface). Then, in this state, the first electromagnetic steel strip and the second electromagnetic steel strip are joined by moving the rotary tool in the joining direction. 2A is a side perspective view, and FIG. 2B is a view taken along the line AA of FIG. 2A.
In the lap joint, as shown in FIG. 2C, at least part of the ends of the first electromagnetic steel strip and the second electromagnetic steel strip are overlapped, and the overlapping portion is pressed while rotating a rotary tool. Then, in this state, the first electromagnetic steel strip and the second electromagnetic steel strip are joined by moving the rotary tool in the joining direction.
In the figure, reference numeral 1 denotes a first electromagnetic steel strip (material to be welded), 2 a second electromagnetic steel strip (material to be welded), 3 a rotating tool, 4 a joint portion, 5 a shoulder, 6 is a probe (pin), 7 is a gripping device, 8 is a surface plate (backing), and 9 is a tip. 2A and 2C, illustration of the gripping device is omitted. In FIG. 2B, the vertical direction is the plate thickness direction, the horizontal direction is the bonding vertical direction (direction of movement of the electromagnetic steel strip), and the direction toward the front side of the paper is the bonding direction.
The first electromagnetic steel strip is the preceding steel strip in the continuous cold-rolling line, and the second electromagnetic steel strip is the following steel strip in the continuous cold-rolling line (an electromagnetic steel strip following the first electromagnetic steel strip). belt).

Butt welding and lap welding are different only in the shape of the unjoined portion, and the configuration of the other devices is basically the same. A case of doing so will be described as an example.

Single-sided friction stir welding uses, for example, a friction stir welding apparatus that includes a rotating tool, a gripping device, and a controller (not shown) that controls the operation of the rotating tool. The controller controls, for example, the tilt angle α of the rotary tool, the position of the tip of the rotary tool, the welding speed, the indentation load, the number of rotations of the rotary tool, and the rotary torque.

In single-sided friction stir welding, a rotating tool is arranged on one surface side of the first and second electromagnetic steel strips, which are the materials to be welded. The first magnetic steel strip and the second magnetic steel strip are placed on a surface plate (backing) so as to be parallel to the joining center line shown in the drawing, and are each held by a holding device. Then, an unjoined portion (to-be-joined region) located on the joining center line, that is, a butt portion between the end (rear end) of the first electromagnetic steel strip and the end (front end) of the second electromagnetic steel strip Then, press while rotating the rotary tool. Then, in that state, the rotary tool is moved in the joining direction. As a result, the materials to be welded are softened by frictional heat between the rotary tool and the first and second electromagnetic steel strips, which are the materials to be welded. Then, by stirring the softened portion with a rotating tool, plastic flow is generated to join the first electromagnetic steel strip and the second electromagnetic steel strip, which are the materials to be joined. A joint portion is formed at the portion where the joining is completed. Also, a thermal processing affected zone is formed adjacent to the joint.

Further, a double-sided friction stir welding method may be performed instead of the single-sided friction stir welding. The double-sided friction stir welding method is a friction stir welding method in which a first magnetic steel strip and a second magnetic steel strip are joined using a pair of rotating tools facing each other. That is, a pair of rotating tools facing each other are pressed from both surfaces of the unjoined portion while being rotated in opposite directions, and in this state, the rotating tools are moved in the joining direction to form the first electromagnetic steel strip and the first. The magnetic steel strips of No. 2 are joined. FIG. 3 (FIGS. 3A and 3B) illustrates a case where butt welding is performed by double-sided friction stir welding. 3A is a side perspective view, and FIG. 3B is a view taken along line AA of FIG. 3A. In the figure, reference numeral 1 is the first electromagnetic steel strip (material to be welded), 2 is the second electromagnetic steel strip (material to be welded), 3-1 is a rotating tool (surface side rotating tool), and 3-2 is rotating. Tool (back side rotary tool), 4 is a joint, 5-1 and 5-2 are shoulders, 6-1 and 6-2 are probes (pins), 7 is a gripping device, 9-1 and 9 -2 is the tip. Note that illustration of the gripping device is omitted in FIG. 3A. In FIG. 3B, the vertical direction is the plate thickness direction, the horizontal direction is the bonding vertical direction (direction of movement of the electromagnetic steel strip), and the direction toward the front side of the paper is the bonding direction.

Double-sided friction stir welding uses, for example, a double-sided friction stir welding apparatus that includes a pair of rotating tools facing each other, a gripping device, and a controller (not shown) that controls the operation of the rotating tools. In the control device, for example, the tilt angle α of the rotary tool, the position of the tip of the rotary tool and the distance between the tips (probes) (hereinafter also referred to as the gap between the probes), the gap between the shoulders of the rotary tool (that is, the distance between the shoulder of the front-side rotary tool and the shoulder of the back-side rotary tool in the plate thickness direction), the welding speed, the pressing load, the number of rotations of the rotary tool, the rotary torque, and the like.

In the double-sided friction stir welding, the rotating tools of the friction stir welding apparatus are arranged on both surfaces of the first and second electromagnetic steel strips, which are the materials to be welded. In addition, the rotating tool arranged on the surface side (upper side in the vertical direction) of the first electromagnetic steel strip and the second electromagnetic steel strip is called a surface side rotating tool, and the first electromagnetic steel strip and the second electromagnetic steel strip A rotary tool arranged on the back side (bottom side in the vertical direction) of the band may be referred to as a back side rotary tool. The first electromagnetic steel strip and the second electromagnetic steel strip are arranged parallel to the joining center line shown in the drawing, and held by a holding device. Then, an unjoined portion (to-be-joined region) located on the joining center line, that is, a butt portion between the end (rear end) of the first electromagnetic steel strip and the end (front end) of the second electromagnetic steel strip are pressed while rotating the rotating tool. Then, in that state, the rotary tool is moved in the joining direction. As a result, the materials to be welded are softened by frictional heat between the rotary tool and the first and second electromagnetic steel strips, which are the materials to be welded. Then, by stirring the softened portion with a rotating tool, plastic flow is generated to join the first electromagnetic steel strip and the second electromagnetic steel strip, which are the materials to be joined. A joint portion is formed at the portion where the joining is completed. Also, a thermal processing affected zone is formed adjacent to the joint.

In the friction stir welding method for an electrical steel strip according to one embodiment of the present invention, the steel structures of the welded portion and the heat-work-affected portion formed by welding each have a ferrite phase-based structure, and the above formula ( It is important to perform bonding under conditions that satisfy the relationships of 1) to (4). As a result, even when an electromagnetic steel strip is used as the material to be joined, the mechanical properties of the coil joint are improved without causing deterioration in the shape of the coil joint, and breakage of the coil joint in the production line is prevented. effectively suppressed.

In order to make the steel structures of the joint formed by joining and the thermal processing affected zone each a ferrite phase-based structure and to satisfy the relationships of the above formulas (1) to (4), for example, When single-sided friction stir welding is performed, the diameter D (mm) of the shoulder portion of the rotating tool satisfies the relationship of the following formula (7), and
RS×D ³ /JS represented by the number of revolutions RS (rotations/minute) of the rotary tool, the diameter D (mm) of the shoulder portion of the rotary tool, and the joining speed JS (mm/min) is given by the following formula (8): Satisfying relationships are preferred.
4 x TJs ≤ D. ≤ 10×TJ (7)
1000×TJ ≤ RS×D ³ /JS ≤ 9000×TJ (8)
where TJ in equations (7) and (8) is
When the unjoined portion is a butt portion, the average value (mm) of the plate thickness of the first electromagnetic steel strip and the plate thickness of the second electromagnetic steel strip,
When the unjoined portion is the overlapping portion, the thickness (mm) of the overlapping portion (that is, the sum of the thickness (mm) of the first electromagnetic steel strip and the thickness (mm) of the second electromagnetic steel strip) is.

That is, by appropriately controlling the diameter D of the shoulder portion of the rotary tool (hereinafter also simply referred to as the shoulder diameter D) according to the thickness of the unjoined portion, A temperature rise due to frictional heat generated between certain first and second electromagnetic steel strips and a shear stress due to frictional force can be effectively imparted to the materials to be joined. Here, if the shoulder diameter D is less than 4×TJ (mm), sufficient plastic flow cannot be obtained, and it may be difficult to satisfy the predetermined relationship. On the other hand, if the shoulder diameter D exceeds 10×TJ (mm), the region where plastic flow occurs unnecessarily widens, and an excessive amount of heat is applied to the joint. As a result, the recrystallized structure of the joint becomes coarse, and it may be difficult to satisfy the predetermined relationship. Therefore, in order to satisfy the condition for satisfying the predetermined relationship, it is preferable that the shoulder diameter D satisfies the relationship of the above formula (7).

Also, RS×D ³ /JS is a parameter that correlates with the amount of heat generated per unit junction length. Then, by setting the range of RS×D ³ /JS to 1000×TJ to 9000×TJ, the rotating tool and the first electromagnetic steel strip and the second electromagnetic steel strip, which are the materials to be welded, are It is possible to effectively apply temperature rise due to frictional heat generated between and shear stress due to frictional force to the materials to be joined. Here, when RS×D ³ /JS is less than 1000×TJ, the calorific value may be insufficient. Therefore, it may be difficult to form a joint interface in a state of being metallurgically joined to the mating surfaces of the first magnetic steel strip and the second magnetic steel strip, making it difficult to satisfy the predetermined relationship. be. On the other hand, when RS×D ³ /JS exceeds 9000×TJ, the amount of heat generated by friction stirring becomes excessive, and an excessive amount of heat is applied to the joint. As a result, the peak temperature (maximum attainable temperature) of the joint increases, the cooling rate decreases, and the recrystallized structure of the joint coarsens. As a result, it may be difficult to satisfy the predetermined relationship. Therefore, from the viewpoint of satisfying the predetermined relationship, it is preferable that RS×D ³ /JS satisfy the relationship of the above formula (8). RS×D ³ /JS is more preferably 1400×TJ or more. Also, RS×D ³ /JS is more preferably 7000×TJ or less.

Further, when performing double-sided friction stir welding, the diameter D (mm) of the shoulder portion of the rotating tool satisfies the relationship of the above formula (7), and
RS×D ³ /JS represented by the number of revolutions RS (rotations/minute) of the rotary tool, the diameter D (mm) of the shoulder portion of the rotary tool, and the joining speed JS (mm/min) is given by the following formula (9): Satisfying relationships are preferred.
200×TJ ≤ RS×D ³ /JS ≤ 2000×TJ (9)
Here, TJ in formula (9) is
When the unjoined portion is a butt portion, the average value (mm) of the plate thickness of the first electromagnetic steel strip and the plate thickness of the second electromagnetic steel strip,
When the unjoined portion is the overlapping portion, the thickness (mm) of the overlapping portion (that is, the sum of the thickness (mm) of the first electromagnetic steel strip and the thickness (mm) of the second electromagnetic steel strip) is.

As described above, RS×D ³ /JS is a parameter that correlates with the amount of heat generated per unit junction length. Then, by setting the range of RS×D ³ /JS to 200×TJ to 2000×TJ, the rotating tool and the first and second electromagnetic steel strips, which are the materials to be welded, are It is possible to effectively apply temperature rise due to frictional heat generated between and shear stress due to frictional force to the materials to be joined. Here, when RS×D ³ /JS is less than 200×TJ, the calorific value may be insufficient. Therefore, it may be difficult to form a joint interface in a state of being metallurgically joined to the mating surfaces of the first magnetic steel strip and the second magnetic steel strip, making it difficult to satisfy the predetermined relationship. be. On the other hand, when RS×D ³ /JS exceeds 2000×TJ, the amount of heat generated by friction stirring becomes excessive, and an excessive amount of heat is applied to the joint. As a result, the peak temperature (maximum attainable temperature) of the joint increases, the cooling rate decreases, and the recrystallized structure of the joint coarsens. As a result, it may be difficult to satisfy the predetermined relationship. Therefore, from the viewpoint of satisfying the predetermined relationship, it is preferable that RS×D ³ /JS satisfies the relationship of the above formula (9). RS×D ³ /JS is more preferably 280×TJ or more. Also, RS×D ³ /JS is more preferably 1600×TJ or less.

In the case of performing double-sided friction stir welding, if the rotation speed RS and/or the shoulder diameter D of the rotating tool are different between the front side rotating tool and the back side rotating tool, the front side rotating tool and the back side rotating tool preferably satisfies the relationships of equations (7) and (9) above.

In addition, the welding conditions such as the inclination angle α of the rotary tool, the number of rotations of the rotary tool, the welding speed, the position of the tip of the rotary tool, the indentation load, and the rotational torque are described in the joint formed by welding and the thermal processing. As long as the steel structures of the affected parts are mainly composed of ferrite phases and the conditions satisfy the relationships of the above formulas (1) to (4), there is no particular limitation, and a conventional method may be followed.

For example, in the case of single-sided friction stir welding, the inclination angle α of the rotating tool is preferably 0°≦α≦4°, more preferably 0°<α≦3°. Here, α is the plate thickness direction of the rotation axis of the rotary tool (hereinafter also referred to as the tool rotation axis) in the plane containing the welding direction and the plate thickness direction (the direction perpendicular to the surface of the workpiece) This is the angle of inclination from (the direction perpendicular to the surface of the material to be joined). In addition, the direction (the angle) in which the tip of the rotary tool precedes the welding direction is defined as +.
The rotational speed of the rotary tool is preferably 100-2000 r/min. By setting the number of revolutions of the rotary tool within this range, it is possible to suppress the deterioration of the mechanical properties due to the application of an excessive amount of heat while maintaining a good surface shape, which is advantageous. The rotational speed of the rotating tool is more preferably 150 r/min or more. Further, the rotational speed of the rotating tool is more preferably 1500 r/min or less.
The bonding speed is preferably 80-600 mm/min. The joining speed is more preferably 100 mm/min or higher. The joining speed is more preferably 500 mm/min or less.
The position of the tip of the rotating tool, the pressing load, the rotating torque, etc. may be appropriately set in accordance with conventional methods.

In the case of double-sided friction stir welding, the inclination angle α of the rotary tools is preferably 0°≦α≦3°, more preferably 0°<α≦2°, for both the front-side rotary tool and the back-side rotary tool. is.
The rotational speed of the rotary tool is preferably 300-9000 r/min. By setting the number of revolutions of the rotary tool within this range, it is possible to suppress the deterioration of the mechanical properties due to the application of an excessive amount of heat while maintaining a good surface shape, which is advantageous. The rotational speed of the rotating tool is more preferably 400 r/min or more. Further, the rotational speed of the rotating tool is more preferably 8000 r/min or less.
The welding speed is preferably 800-5000 mm/min. The joining speed is more preferably 1000 mm/min or more. The joining speed is more preferably 4000 mm/min or less.
The position of the tip of the rotary tool, the load to be pushed, the rotational torque, the gap between the probes, the gap between the shoulders of the rotary tool, and the like can be appropriately set in accordance with conventional methods.

As shown in FIG. 3, when performing double-sided friction stir welding, the rotating direction of the front side rotating tool and the rotating direction of the back side rotating tool are determined from the front side (or back side) of the workpiece. It is preferable that the rotation speed is the same. As a result, the rotational torques applied to the workpieces from the front-side rotating tool and the back-side rotating tool can be canceled out. As a result, it is possible to simplify the structure of the jig for restraining the materials to be welded, compared to the single-sided friction stir welding method in which the unwelded parts are pressed from one side to be welded.

In addition, if the rotating direction of the front side rotating tool and the rotating direction of the back side rotating tool are the same when viewed from the front side (or back side) of the work to be welded, the relative position of one rotating tool to the other rotating tool is Velocity approaches zero. As a result, the plastic flow of the material to be joined approaches a homogeneous state, and plastic deformation is reduced. As a result, heat generation due to plastic deformation of the material cannot be obtained, making it difficult to achieve a good bonding state. Therefore, from the viewpoint of uniformly obtaining sufficient temperature rise and shear stress in the thickness direction of the material to be welded to achieve a good welding state, the rotation direction of the front side rotary tool and the rotation of the back side rotary tool It is preferable that the direction is the opposite direction when viewed from the surface side (or the back side) of the material to be joined.

In addition, with regard to the rotary tool used for friction stir welding, the steel structure of the joint formed by welding and the steel structure of the heat-affected zone are each a structure mainly composed of ferrite phase, and the above formulas (1) to (4) is not particularly limited as long as it satisfies the relationship of
For example, the tip of the rotating tool contacts the first and second electromagnetic steel strips, which are the materials to be joined, during joining. Therefore, the tip of the rotary tool is made of a material harder than the first and second magnetic steel strips in a high-temperature state exposed during joining. As a result, the rotary tool can apply deformation to the first and second magnetic steel strips while maintaining the shape of the tip portion during joining. As a result, it is possible to achieve a high agitation performance continuously, and proper joining becomes possible. The hardness of the tip portion of the rotary tool, the first magnetic steel strip and the second magnetic steel strip may be measured by a high temperature Vickers hardness test method and compared. Note that only the tip of the rotating tool may be made of a material harder than the first and second magnetic steel strips. Also, the entire rotary tool may be made of a harder material than the first electromagnetic steel strip and the second electromagnetic steel strip.

4 (FIGS. 4A to 4C) show examples of rotating tools used in single-sided friction stir welding. As shown in FIG. 4, the rotating tool used in single-sided friction stir welding has a tip portion of the rotating tool that is arranged on a shoulder portion (the range indicated by the shoulder diameter in the figure) and on the shoulder portion. and a probe (range indicated by the pin diameter in the figure) sharing the shoulder and the rotation axis.
In the example of the rotary tool shown in FIG. 4A, the shape of the rotary tool is shoulder diameter D: 13 mm, probe diameter (hereinafter also referred to as pin diameter): 4 mm, probe length (hereinafter also referred to as pin length): 1.8 mm, concave depth (not shown): 0.3 mm.
In the example of the rotary tool shown in FIG. 4B, the shape of the rotary tool is shoulder diameter D: 18 mm, pin diameter: 5.5 mm, pin length: 2.1 mm, concave depth (not shown): 0.3 mm. be.
In the example of the rotating tool shown in FIG. 4C, the shape of the rotating tool is shoulder diameter D: 21 mm, pin diameter: 6.7 mm, pin length: 2.4 mm, concave depth (not shown): 0.3 mm. be.

5 (FIGS. 5A to 5C) show examples of rotating tools used in double-sided friction stir welding.
In addition, as shown in FIG. 5, the rotating tool used in double-sided friction stir welding also has a shoulder portion (the range indicated by the shoulder diameter in the figure) and a tip portion of the rotating tool. and a probe (range indicated by the pin diameter in the figure) sharing the shoulder and the rotation axis.
In the example of the rotary tool shown in FIG. 5A, the shape of the rotary tool is shoulder diameter D: 13 mm, pin diameter: 4 mm, pin length: 0.6 mm, concave depth (not shown): 0.6 mm.
In the example of the rotating tool shown in FIG. 5B, the shape of the rotating tool is shoulder diameter D: 18 mm, pin diameter: 5.5 mm, pin length: 0.8 mm, concave depth (not shown): 0.3 mm. be.
In the example of the rotating tool shown in FIG. 5C, the shape of the rotating tool is shoulder diameter D: 21 mm, pin diameter: 6.7 mm, pin length: 0.9 mm, concave depth (not shown): 0.3 mm. be.

As shown in FIGS. 4 and 5, the tip of a typical rotary tool consists of a shoulder (range indicated by the shoulder diameter in the figures) and a probe (range indicated by the pin diameter in the figures). The shoulder portion has a flat shape formed by a substantially flat surface or a gently curved surface. The shoulder has a function of generating frictional heat by contacting the first and second magnetic steel strips while rotating during joining. In addition, the shoulder has a function of pressing the portion softened by heat to prevent the material from scattering and promoting plastic flow in the direction of rotation. The probe has a shape that is discontinuous with the shoulder portion, and has a shape that protrudes substantially perpendicularly toward the workpiece (not shown). The probe has a function of improving the stirring ability near the center of the thickness of the sheet by penetrating the softened portions of the first and second magnetic steel strips toward the center of the thickness during welding. Also, the probe is usually centrally located on the shoulder.

The shoulder diameter D (mm) is not particularly limited. From the viewpoint of the conditions for satisfying the relationships of formulas (1) to (4), it is preferable to satisfy the relationships of formulas (7) to (9).

Also, the pin diameter and pin length of the rotary tool are not particularly limited, and may be appropriately set according to a conventional method. For example, when butt-joining a first electromagnetic steel strip and a second electromagnetic steel strip having different thicknesses, the average value of the thicknesses of the first and second electromagnetic steel strips is considered. Then, the pin diameter, pin length, etc. of the rotary tool can be set according to the usual method. Further, when lap-joining the first electromagnetic steel strip and the second electromagnetic steel strip, the total thickness of the first and second electromagnetic steel strips is taken into consideration, and a conventional method is followed. Then, the pin diameter and pin length of the rotary tool can be set.

Conditions other than the above are not particularly limited, and may be carried out according to conventional methods.

[3] Method for producing an electromagnetic steel strip Next, a method for producing an electromagnetic steel strip according to one embodiment of the present invention will be described.
A method for manufacturing an electromagnetic steel strip according to one embodiment of the present invention comprises:
a step of joining the first magnetic steel strip and the second magnetic steel strip by the friction stir welding method for magnetic steel strips according to one embodiment of the present invention to obtain a joined steel strip;
and cold-rolling the joined steel strip to obtain a cold-rolled steel strip.
Here, the joined steel strip preferably has a first electromagnetic steel strip, a second electromagnetic steel strip, and a joining joint of the electromagnetic steel strip according to the embodiment of the present invention. and the second electromagnetic steel strip are joined via the joining joint of the electromagnetic steel strip according to one embodiment of the present invention.
Also, the cold rolling conditions are not particularly limited, and may be in accordance with conventional methods. Optionally, pickling may also be performed prior to cold rolling.

Hereinafter, the action and effects of the present invention will be described using examples. In addition, the present invention is not limited to the following examples.

The electromagnetic steel strips having the composition shown in Table 1 (the balance being Fe and unavoidable impurities) were used as the materials to be joined (first and second electromagnetic steel strips), and the conditions shown in Tables 2 and 3 By friction stir welding, the first electromagnetic steel strip (preceding steel strip) and the second electromagnetic steel strip (following process) are joined by simulating being on a continuous cold rolling line, and the electromagnetic steel strip was manufactured. Here, in the case of butt joint, the groove is a so-called I-shaped groove that does not have a groove angle on the end faces of the two electromagnetic steel strips that are the materials to be joined, and the two electromagnetic steel strips are joined in a milling-like surface condition. The steel strips were butted and joined together (the same is true for Table 4, which will be described later). Table 1 also shows the average ferrite grain size, the average hardness, and the Erichsen value of the base material of the magnetic steel strip. Here, the average value of ferrite grain size and the average value of hardness of the base metal portion of the electrical steel strip are obtained by the above-described method. The Erichsen value is a value measured according to the Erichsen test method defined in JIS Z 2247. In addition, the conditions not specified were set according to the ordinary method.

In the single-sided friction stir welding, as shown in FIG. 2A, in the case of butt welding, the rotating tool was rotated clockwise when viewed from above in the vertical direction (counterclockwise when the tip of the rotating tool was viewed from the front). Also, any of the three types of rotary tools with cross-sectional dimensions and shapes shown in FIG. 4 were used. These rotating tools are all made of tungsten carbide (WC) with a Vickers hardness of HV1090, which is harder than the material to be joined. Further, when the plate thicknesses of the first electromagnetic steel strip and the second electromagnetic steel strip are different, the butted portion of the first electromagnetic steel strip and the second electromagnetic steel strip faces the back surface (the surface on the surface plate side). The surface (the surface on which the rotary tool is arranged) was made to have a step.
In the case of lap joint, as shown in FIG. 2C, the first electromagnetic steel strip (leading steel strip) is placed on the upper side of the stack, and the second magnetic steel strip (following steel strip) is placed on the bottom side of the stack. spliced. The direction of rotation of the rotating tool, the shape of the rotating tool, and the like are the same as in the case of butt joint.

In the double-sided friction stir welding, in the case of butt welding, as shown in FIG. The back-side rotating tool was rotated counterclockwise when viewed from the vertical upper side. In other words, both were rotated counterclockwise when the tip of each rotating tool was viewed from the front. Also, any of the three types of rotary tools with cross-sectional dimensions and shapes shown in FIG. 5 were used. In addition, rotary tools having the same cross-sectional dimensions and shape were used as the front-side rotating tool and the back-side rotating tool. These rotating tools are all made of tungsten carbide (WC) with a Vickers hardness of HV1090, which is harder than the material to be joined. Further, when the plate thicknesses of the first electromagnetic steel strip and the second electromagnetic steel strip are different, the abutting portion of the first electromagnetic steel strip and the second The surface (on the side where the surface-side rotating tool is arranged) was set to have a stepped state.
In the case of lap joint, the first electromagnetic steel strip (preceding steel strip) was joined to the upper side of the lap, and the second magnetic steel strip (following steel strip) was joined to the lower side of the lap. The direction of rotation of the rotating tool, the shape of the rotating tool, and the like are the same as in the case of butt joint.

Also, for comparison, the materials to be joined (the first electromagnetic steel strip and the second electromagnetic steel strip) shown in Table 4 were laser-welded under the conditions shown in Table 4, and the first electromagnetic steel strip and A second electromagnetic steel strip was joined to produce a joint of the electromagnetic steel strips.

A CO2 laser oscillator with a maximum output of 5.5 kW was used in laser welding. Helium was used as the shielding gas, and the flow rate of the shielding gas was 40 liters/minute. Welding was performed without using a filler wire when the "filler wire addition" in Table 4 was "no". In Table 4, when "Addition of filler wire" is "Yes", MIG wire (0.9 mmφ) having the composition shown in Table 5 (the balance being Fe and unavoidable impurities) was used as the filler wire. , are welded.

It should be noted that all of the joints of the electromagnetic steel strips obtained as described above were in a sound state with no defects in both the external appearance and the internal surface.

For the thus-obtained welded joint of the electromagnetic steel strips, a welded portion, a thermal processing-affected portion, and a base material portion were defined according to the procedure described above.
In addition, according to the above-mentioned points,
Dsz: average value of ferrite grain size at the junction (μm);
Dhaz1: average value (μm) of ferrite grain size in the heat-affected zone on the first electromagnetic steel strip side;
Dhaz2: average value (μm) of ferrite grain size in the heat-affected zone on the second electromagnetic steel strip side;
Dbm1: average value (μm) of ferrite grain size in the base metal portion of the first electrical steel strip;
Dbm2: average value (μm) of ferrite grain size in the base metal portion of the second electromagnetic steel strip;
Hsz: average hardness of the joint,
Hbm1: Average hardness of the base metal portion of the first magnetic steel strip Hbm2: Average hardness of the base metal portion of the second magnetic steel strip was measured.
Furthermore, in the vertical cut plane of the joint of the obtained electromagnetic steel strip (the plane shown in FIG. 1 (that is, the plane including the joint vertical direction and the plate thickness direction)), TszL: the thickness of the joint Minimum value (mm) and TszH: The maximum value (mm) of the joint thickness was measured.
In addition, in the welded joint of the electromagnetic steel strip obtained by laser welding, the above measurement was performed by regarding the welded part as the welded part and the heat-affected zone as the heat-affected zone. It is the same as the case of the joint of the electromagnetic steel strip obtained by.).
Results are shown in Tables 6 and 7.

In addition, the obtained welded joints of the electromagnetic steel strips were evaluated for the effect of suppressing breakage of the coil joints in the production line (hereinafter also referred to as "breakage suppressing effect").

That is, the joint of the obtained electromagnetic steel strip includes the joint, the thermal processing affected zone and base metal on the first electromagnetic steel strip side, and the thermal processing affected zone and base metal on the second electromagnetic steel strip side. A test piece was taken as follows. Then, using the sampled test piece, the Erichsen value of the bonded joint was measured according to the Erichsen test method specified in JIS Z 2247. Then, the ratio of the Erichsen value of the joined joint to the Erichsen value of the base material portion (hereinafter also referred to as the ratio of the Erichsen value) was used to evaluate the fracture prevention effect according to the following criteria. Table 8 shows the results.
[Ratio of Erichsen value (%)] = [Erichsen value of joined joint] / [Erichsen value of base material part] × 100
○ (accepted): Erichsen value ratio of 80% or more × (failed): Erichsen value ratio of less than 80% When the Erichsen value of the base metal portion is different, the Erichsen value of the base metal portion is the smaller one of the Erichsen value of the base metal portion of the first electromagnetic steel strip and the Erichsen value of the base metal portion of the second electromagnetic steel strip. value.

From Table 8, it can be seen that the steel structures of the joint and the heat-work-affected zone are ferrite phase-based structures, respectively, and all of the invention examples that satisfy the relationships of the above formulas (1) to (4) exhibit excellent rupture. had a deterrent effect.
On the other hand, in the comparative example, the steel structure of the joint and the heat-affected zone is not a structure mainly composed of ferrite phase and / or does not satisfy at least one of the relationships of the above formulas (1) to (4). However, no significant breakage prevention effect was obtained.

1 First electromagnetic steel strip (material to be joined)
2 Second electromagnetic steel strip (material to be joined)
3 Rotating tool 3-1 Rotating tool (surface side rotating tool)
3-2 Rotating tool (back side rotating tool)
4 Joint 4-1 Thermal processing affected zone (first electromagnetic steel strip side)
4-2 Thermal processing affected zone (second electromagnetic steel strip side)
5, 5-1, 5-2 shoulder 6, 6-1, 6-2 probe 7 gripping device 8 surface plate (backing)
9, 9-1, 9-2 tip

Claims (6)

An electromagnetic steel strip joining joint for joining a first electromagnetic steel strip and a second electromagnetic steel strip,
The joint of the electromagnetic steel strip has a joint and a thermal processing affected zone adjacent to the joint,
The steel structures of the joint and the thermal processing affected zone are structures mainly composed of ferrite phase,
A joint for electromagnetic steel strips that satisfies the relationships of the following formulas (1) to (4).
Dsz≦200 μm (1)
Dhaz1≦Dbm1 (2)
Dhaz2≦Dbm2 (3)
0.9×(Hbm1+Hbm2)/2≦Hsz≦1.2×(Hbm1+Hbm2)/2 (4)
here,
Dsz is the average value (μm) of the ferrite grain size at the junction;
Dhaz1 is the average value (μm) of the ferrite grain size in the heat-affected zone on the first electromagnetic steel strip side;
Dhaz2 is the average value (μm) of the ferrite grain size in the heat-affected zone on the second electromagnetic steel strip side;
Dbm1 is the average value (μm) of the ferrite grain size in the base metal portion of the first electromagnetic steel strip;
Dbm2 is the average value (μm) of the ferrite grain size in the base metal portion of the second electromagnetic steel strip;
Hsz is the average hardness of the joint,
Hbm1 is the average hardness of the base metal portion of the first magnetic steel strip, and Hbm2 is the average hardness of the base metal portion of the second magnetic steel strip. 2. The joint for electromagnetic steel strips according to claim 1, which satisfies the following equations (5) and (6).
0.8×TbmL≦TszL (5)
TszH≦1.3×TbmH (6)
here,
TszL is the minimum thickness of the joint (mm);
TszH is the maximum thickness of the joint (mm);
TbmL is the plate thickness (mm) of the thinner one of the first magnetic steel strip and the second magnetic steel strip,
TbmH is the plate thickness (mm) of the thicker magnetic steel strip of the first magnetic steel strip and the second magnetic steel strip;
is. However, when the plate thicknesses of the first magnetic steel strip and the second magnetic steel strip are the same, TbmL=TbmH. A friction stir welding method for an electromagnetic steel strip, which joins a first electromagnetic steel strip and a second electromagnetic steel strip following the first electromagnetic steel strip in a continuous cold rolling line, comprising:
Pressing a rotating tool against the butted portion or the unjoined portion, which is the overlapping portion, between the end portion of the first electromagnetic steel strip and the end portion of the second electromagnetic steel strip, and
Next, by moving the rotary tool in the joining direction, the first electromagnetic steel strip and the second electromagnetic steel strip are joined,
The steel structures of the joined portion and the heat-affected zone formed by joining the first electromagnetic steel strip and the second electromagnetic steel strip each have a structure mainly composed of ferrite phase, and the following equations (1) to ( 4) A friction stir welding method for electromagnetic steel strips, wherein welding is performed under conditions that satisfy the relationship of 4).
Dsz≦200 μm (1)
Dhaz1≦Dbm1 (2)
Dhaz2≦Dbm2 (3)
0.9×(Hbm1+Hbm2)/2≦Hsz≦1.2×(Hbm1+Hbm2)/2 (4)
here,
Dsz is the average value (μm) of the ferrite grain size at the junction;
Dhaz1 is the average value (μm) of the ferrite grain size in the heat-affected zone on the first electromagnetic steel strip side;
Dhaz2 is the average value (μm) of the ferrite grain size in the heat-affected zone on the second electromagnetic steel strip side;
Dbm1 is the average value (μm) of the ferrite grain size in the base metal portion of the first electromagnetic steel strip;
Dbm2 is the average value (μm) of the ferrite grain size in the base metal portion of the second electromagnetic steel strip;
Hsz is the average hardness of the joint,
Hbm1 is the average hardness of the base metal portion of the first magnetic steel strip, and Hbm2 is the average hardness of the base metal portion of the second magnetic steel strip. 4. The friction stir welding method for electromagnetic steel strips according to claim 3, wherein the welding is performed under conditions satisfying the relationships of the following expressions (5) and (6).
0.8×TbmL≦TszL (5)
TszH≦1.3×TbmH (6)
here,
TszL is the minimum thickness of the joint (mm);
TszH is the maximum thickness of the joint (mm);
TbmL is the plate thickness (mm) of the thinner one of the first magnetic steel strip and the second magnetic steel strip,
TbmH is the plate thickness (mm) of the thicker magnetic steel strip of the first magnetic steel strip and the second magnetic steel strip;
is. However, when the plate thicknesses of the first magnetic steel strip and the second magnetic steel strip are the same, TbmL=TbmH. 5. The friction stir welding method for electrical steel strips according to claim 3 or 4, wherein the method is double-sided friction stir welding. a step of joining a first electromagnetic steel strip and a second electromagnetic steel strip by the friction stir welding method for electromagnetic steel strips according to any one of claims 3 to 5 to obtain a joined steel strip;
cold-rolling the joined steel strip to obtain a cold-rolled steel strip.

Images